The present disclosure generally relates to vehicle service equipment and methodology and, more specifically, to system and method for measuring caster trail of a vehicle.
It is important to ensure that parameters related to the steering system and/or wheels of a vehicle are within specifications provided by vehicle manufacturers. If the parameters do not match with the values specified in the specifications, there may be excessive or uneven wear on the wheels. In addition, the performance of the vehicle, particularly handling and stability, may be adversely affected.
During vehicle service, various ways and systems are used to determine parameters related to the steering system and/or wheels of a vehicle. For example, during alignment of an automotive vehicle, a vision imaging system having optical sensing devices, such as cameras, may be used to determine the positions or positional characteristics of various objects on the vehicle and/or to obtain positional and angular orientation information about the vehicle. The information includes toe angles, caster values, camber angles, frame symmetries, etc.
However, it has been found that conventional position determination systems are not able to provide readings of certain parameters, such as caster trail. The definition of caster trail is illustrated in FIG. 1. FIG. 1 shows a side view of a steerable wheel of a vehicle. The steering axis 14 passes through steering pivots 15a and 15b of the wheel 22. Caster trail 10 is defined as the distance between the intersection of a steering axis 14 of the wheel 22 and a ground plane 16, and the intersection of side centerline 50 and the ground plane 16, as viewed from the side of the vehicle. The side centerline 50 is a line normal to the reference plane 16 and passing through the wheel center 19. Alternatively, although less commonly used, caster trail can also be defined as the fore and after distance between the center of the wheel and the intersection of the steering axis 14 with a reference plane that is at the height of the wheel center 19 and parallel to the ground plane 16.
If a vehicle""s caster trail does not match up with a manufacturer""s specifications, the mismatch may be an indication of mis-adjustment or damage to the vehicle""s suspension and/or steering system. Therefore, there is a need for a system and method for measuring the caster trail of the wheels on a vehicle. There is also a need to determine whether the measured caster trail of a vehicle matches the specifications provided by vehicle makers.
An exemplary system for determining caster trail includes a data processing system, such as a computer, and position sensing devices for obtaining positional signals representing positional parameters of the wheel. The wheel center may be determined based on the wheel axis, the spindle, the contact patch, or other elements that can be used to determine the position of the wheel center.
The data processing system then determines a projection of the wheel center on the reference plane, and an intersection of the reference plane and the steering axis or an extension thereof. The system then determines the caster trail based on distance between the projection of the wheel center on the reference plane and the intersection.
The position sensing devices may include optical imaging devices or weight sensing devices or any other types of devices that are well known to people skilled in the art to obtain positional parameters of objects. Optical sensing devices may include video cameras, light sensors, and/or the like. The optical sensing devices form a viewing path with the wheel directly or with a target attached to the wheel. The weight sensing devices may include gravity gauges mounted to the wheel.
The reference plane is chosen based on the definition of the caster trail and preference of system design. For example, the reference plane may be set as the plane on which the wheel is positioned, a plane passing the wheel center and parallel to the plane on which the wheel is positioned, or any other plane that can be used to derive the caster trail.
The data processing system includes a data storage device, such as a hard disk drive, that includes instructions upon execution by a data processor in the data processing system to cause the data processing system to perform programmed functions.
In one aspect, the system determines caster trail based on well-known parameters related to the steering axis, such as caster values. According to a further aspect, the system may access a database including specifications of caster trail of the vehicle under test. The system may determine whether the calculated caster trail is within certain margin of the specifications. Furthermore, the system may obtain scrub radius of the wheel and compare with scrub radius specifications. Optionally, a graphical and/or numeric screen showing measurement results and specifications may be presented to the operator of the system to assist determination of the operational status of the wheel.
Described also is a machine-readable medium carrying one or more sequences of instructions which, when executed by at least one processor, cause the processor to determine caster trail based on positional characteristics of a steering axis of the wheel, a reference plane and a wheel center.
Additional aspects and advantages of the present disclosure will become readily apparent to those skilled in this art from the following detailed description, wherein only an exemplary embodiment of the present disclosure is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present disclosure. As will be realized, the present disclosure is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.